Dopamine (DA) innervation of the afferent basal ganglia, the caudate and putamen, is well established and essential to selected motor and cognitive processes(1). By contrast, the existence and function of DA pathways to the subthalamic nucleus (STN) and other key efferent nuclei of the basal ganglia are still obscure. Nonetheless, recent investigations suggest this innervation is histochemically dense, and by its location, strategically situated to potentially modulate striatal outflow(9,14,26) . As a first step in elucidating the role of DA innervation of striatal outflow, we will study the anatomy, biochemistry and behavioral pharmacology of the DA projections to STN in the rat, a nucleus known to play a key role in modulation of normal and abnormal motor function in rodents and mammals (14,28).